Message-ID: <8f13aa62-6360-8038-3041-86fd51b40a3e@linux.ibm.com>
Date:   Tue, 11 Jan 2022 09:40:05 +0100
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Subject: Re: [PATCH net 3/3] net/smc: Resolve the race between SMC-R link
 access and clear
Content-Language: en-US
To:     Wen Gu <guwen@linux.alibaba.com>, davem@davemloft.net,
        kuba@kernel.org
Cc:     linux-s390@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <1641806784-93141-1-git-send-email-guwen@linux.alibaba.com>
 <1641806784-93141-4-git-send-email-guwen@linux.alibaba.com>
From:   Karsten Graul <kgraul@linux.ibm.com>
Organization: IBM Deutschland Research & Development GmbH
In-Reply-To: <1641806784-93141-4-git-send-email-guwen@linux.alibaba.com>
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Precedence: bulk

On 10/01/2022 10:26, Wen Gu wrote:
> @@ -1226,15 +1245,23 @@ void smcr_link_clear(struct smc_link *lnk, bool log)
>  	smc_wr_free_link(lnk);
>  	smc_ib_destroy_queue_pair(lnk);
>  	smc_ib_dealloc_protection_domain(lnk);
> -	smc_wr_free_link_mem(lnk);
> -	smc_lgr_put(lnk->lgr); /* lgr_hold in smcr_link_init() */
>  	smc_ibdev_cnt_dec(lnk);
>  	put_device(&lnk->smcibdev->ibdev->dev);
>  	smcibdev = lnk->smcibdev;
> -	memset(lnk, 0, sizeof(struct smc_link));
> -	lnk->state = SMC_LNK_UNUSED;
>  	if (!atomic_dec_return(&smcibdev->lnk_cnt))
>  		wake_up(&smcibdev->lnks_deleted);

Same here, waiter should not be woken up until the link memory is actually freed.

> +	smcr_link_put(lnk); /* theoretically last link_put */
> +}
> +
> +void smcr_link_hold(struct smc_link *lnk)
> +{
> +	refcount_inc(&lnk->refcnt);
> +}
> +
> +void smcr_link_put(struct smc_link *lnk)
> +{
> +	if (refcount_dec_and_test(&lnk->refcnt))
> +		__smcr_link_clear(lnk);
>  }